EPSC
EPSC Abstracts
Vol. 8, EPSC2013-751, 2013
European Planetary Science Congress 2013
c Author(s) 2013
European Planetary Science Congress
Nitrogen, Carbon, and Noble Gases in Apollo Lunar
Samples
J. Mortimer (1), A. B. Verchovsky (1), and M. Anand (1,2)
(1) Planetary and Space Sciences, Dept. of Physical Science, The Open University, Milton Keynes, MK7 6AA, UK; (2) Dept.
of Earth Sciences, The Natural History Museum, London, SW7 5BD, UK; (Email: [email protected])
Abstract
1.1 ‘Finesse’ Mass Spectrometer System
A suite of five powdered lunar basalt samples have
been analysed for nitrogen, carbon, helium, neon, and
argon, using a high-sensitivity stepped combustion
mass spectrometer system at the Open University,
UK. Preliminary results indicate the presence of
cosmogenic nitrogen and carbon, released in small
amounts at high temperatures, as well as small
amounts of cosmogenic neon and argon (mixed with
a trapped non-cosmogenic component). Low
temperature steps are dominated by contamination
release, although 15555 displays an unusually
abundant, isotopically light carbon component,
released at 500 °C.
Finesse is a custom-built, automated stable isotope
machine, located at the Open University, UK. It
consists of three static-mode mass spectrometers (one
for carbon, one for nitrogen, and a quadrupole for
noble gases), all linked to a common sample
inlet/extraction furnace system, and operating under
high vacuum [5]. Very low blank levels associated
with Finesse make it ideal for the analysis of lowabundance volatiles typically found in lunar samples.
1. Introduction
In recent years, the search for lunar volatiles has
attracted renewed interest; new analyses of lunar
glasses and apatite crystals suggest initial magma
volatile contents (prior to degassing) many times
higher than previously reported [1], with some
possibly reaching terrestrial-like volatile abundances
[2]. Alongside these discoveries, several spacecraft
have carried out remote experiments on the lunar
surface, with equally encouraging results. The Moon
Mineralogy Mapper (M3) spectrometer on-board
Chandrayaan-1 detected absorptions of wavelengths
associated with the presence of either OH or H2O
groups within the upper layers of the lunar regolith
[3]. Most recently, the LCROSS mission documented
water and other hydrocarbons and volatiles within
impact ejecta near the lunar south pole [4]. In light
of this, and given the advancements in analytical
techniques made in the decades since the Apollo
missions returned lunar samples to Earth, it seems
timely to reassess the volatiles in lunar samples, to
better constrain their likely source(s) and abundances.
Using The Open University’s custom-built highsensitivity mass spectrometer system (‘Finesse’),
stepped combustion analyses have been carried out
on a range of lunar basalts. Stable isotope data for
carbon, nitrogen, helium, neon, and argon has been
collected for each combustion step, and the
preliminary results are presented herein.
2. Methods
Five powdered lunar basalts were selected for initial
analyses, one each from Apollo 11, 12, 14, 15, and
17. For each sample, 5 mg of basalt powder were
measured out and placed into handmade platinum foil
‘buckets’
(previously
cleaned
to
remove
contamination), which were then crushed to form
spheres for ease of sample introduction. Empty Pt
foil buckets were used to measure machine blank
levels.
Samples were dropped into the furnace and
combusted (in 100 °C steps, from 200 °C to 1400 °C);
the gases released at each temperature step passed
through a series of cold fingers, cryotraps, and
molecular sieves to separate and purify them, before
they being sequentially fed through into the relevant
mass spectrometer. In these initial analyses, data
were collected for N2, CO2, He, Ne, and Ar.
3. Preliminary Results
3.1 Nitrogen
Most of the nitrogen in the samples analysed so far
was released at lower temperature steps (typically <
500 °C), and was associated with δ15N values of ±
10 ‰ or less. Mid-temperature nitrogen (600900 °C), while much less abundant, has similar δ15N
values of between -10 ‰ to +40 ‰. However, at
temperatures above 900 °C, the nitrogen released is
at, or is below, blank levels, with δ15N values of
+500 ‰ to +1000 ‰.
3.2 Carbon
As with nitrogen, the majority of the carbon in the
basalts is released at temperatures below 500-600 °C,
associated with δ13C values of -35 ‰ to -9 ‰. Very
little carbon (only just above blank levels) is released
above 600 °C, although, similar to nitrogen, the
carbon becomes isotopically heavier at the higher
temperature steps (+ 900 °C), peaking at slightly
positive δ13C values of between +2 ‰ and +6 ‰.
In 15555, a distinct carbon component is released
between 500-600 °C, with a much lighter isotopic
signature of -46 ‰. This light carbon component is
present in far greater abundance than seen in other
samples, at around 5200 ng, and compared to other
low-temperature carbon components in the same
sample, at around 500 ng (Figure 1). Apart from this
light component, the isotopic values for carbon in
15555 at other temperature steps match well with
published stepped combustion data for this sample
[6].
level amounts, suggests spallation processes are the
most likely source for such high-temperature
nitrogen; the heaviest isotopic composition recorded
for nitrogen is in 10017, with the greatest exposure
age (at 480 My [7]). Carbon displays a similar
enrichment in the heavy isotope at high temperatures,
although not to the same extent. Furthermore,
cosmogenic neon and argon are also present in these
samples.
The trapped noble gas components seen in the
samples do not seem to be from a solar wind source.
The variable nature of the isotopic signatures of the
volatiles released below 500-600 °C, and the relative
abundance of gas released at these temperatures,
indicates a mixing of different terrestrial
contaminants, loosely bound to the samples.
Further analyses of lunar basalt chips, and the
analysis of more pristine samples (i.e. those with <
50 My exposure ages) are planned, to better identify
and characterize indigenous lunar carbon, nitrogen,
and noble gas components.
Acknowledgements
We wish to thank F. A. J. Abernethy, who has
provided help and advice relating to the running of
samples in Finesse. We also thank R. Tartèse for
useful discussions about lunar basalts and volatiles.
We thank CAPTEM for allocation of lunar samples.
JM thanks STFC and the Open University for a PhD
studentship. This work has been partially funded by
STFC (grant number ST/I001298/1 to MA).
References
Figure 1: Step plot for carbon released from
powdered basalt sample 15555.
3.3 Noble Gases
Initial results indicate an excess of neon and argon in
the basalt samples analysed so far; both neon and
argon display mixing between a minor cosmogenic
component, and a more abundant non-cosmogenic
trapped component. 4He is released in the 500 °C
step, and is correlated with a release of 20Ne.
4. Summary
From these preliminary results, a striking feature is
the high-temperature release of isotopically very
heavy nitrogen in the samples analysed so far. Such
isotopically heavy nitrogen, present in almost blank-
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